VAX1 mutation associated with microphthalmia, corpus callosum agenesis, and orofacial clefting: the first description of a VAX1 phenotype in humans.

Department of Pediatrics, Division of Genetics, University of California, San Francisco, California 94143-0748, USA. slavotia@peds.ucsf.edu

Abstract

Vax1 and Vax2 have been implicated in eye development and the closure of the choroid fissure in mice and zebrafish. We sequenced the coding exons of VAX1 and VAX2 in 70 patients with anophthalmia/microphthalmia (A/M). In VAX1, we observed homozygosity for two successive nucleotide substitutions c.453G>A and c.454C>A, predicting p.Arg152Ser, in a proband of Egyptian origin with microphthalmia, small optic nerves, cleft lip/palate, and corpus callosum agenesis. This mutation affects an invariant residue in the homeodomain of VAX1 and was absent from 96 Egyptian controls. It is likely that the mutation results in a loss of function, as the mutation results in a phenotype similar to the Vax1 homozygous null mouse. We did not identify any mutations in VAX2. This is the first description of a phenotype associated with a VAX1 mutation in humans and establishes VAX1 as a new causative gene for A/M.

A. Chromatogram from the proband and a control, showing homozygosity for c.453G>A and c.454C>A (c.453_454delinsAA) in the proband (marked by arrows). B. Frontal view of the proband, showing bilateral severe microphthalmia. C. Frontal view of the proband, showing bilateral cleft lip. D. Mutated VAX1 cannot activate endogenous dnTCF7L2. As determined by Q-RTPCR, the expression of full-length TCF7L2 mRNA (exons 5-6) is not affected by overexpression of the human wild-type VAX1 in HEK293 cells, while the expression of dnTCF7L2 (exons 1b-6) is induced. This induction is not seen with mutated VAX1. Fold change is the ratio between expression normalized to GAPDH in cells transfected with the wild-type VAX1 expression construct versus cells transfected with the mutated VAX1 expression construct. Error bars are mean ± standard deviation (n = 3).